1. Field of the Invention
The present invention relates to a drilling head of a rock drill for use in a rotary-percussion power tool for removing stone and stone-like material such as, e.g., concrete.
2. Description of the Prior Art
Rock drills, which are used in hand-held power tool, have, at one end of their stems, a shank and, at the other, opposite end, a drilling head with cutting elements formed of a hard material. The cutting elements are usually formed as cutting plates or bits. Alternatively, the entire drilling head with the cutting elements can be formed of a hard material. A drawback of this type of drilling heads consists in that upon striking a reinforcing metal during the drilling of concrete, the cutting edges are subjected to an increased load. This is particularly the case when the drilling heads are formed with a pointed wedge angle that is particularly suitable for an increased drilling capacity of the tool.
British Publication GB 530113A discloses a drilling head of a rock drill having a main cutting plate and two auxiliary cutting plates radially offset relative to the main cutting plate and having their cutting edges extending parallel to each other.
European Publication EP 607958A1 discloses a rock drill in which two auxiliary cutting plates, which have their cutting edges extending parallel to each other, are radially spaced from the main cutting plate by different distances.
U.S. Pat. No. 5,492,187 discloses a rock drill with a compact drilling head formed entirely of a hard material. The drilling head has a diametrically extending main bit and two auxiliary bits which are provided exclusively in radially outer region. The auxiliary bits trail the main bit and extend at an acute angel in the drilling direction. The cutting edges of the auxiliary bits extend radially. Because of a rapid wear of the main bit, which is arranged axially in front of the auxiliary bits, the axial distance between the main bit and the auxiliary bits becomes reduced which, in turn, reduces the drilling capacity of the drill and its service life.
Accordingly, an object of the present invention is to increase the service life of a drilling head.
Another object of the present invention is to reduce the danger of the drilling head being fractured upon striking reinforcing metal.